Recently, a large number of In2O3-based oxide semiconductors (mainly Indium Zinc Oxide - IZO and Indium Gallium Zinc Oxide - IGZO) have been extensively investigated for use as the semiconducting channels in thin film transistors (TFTs). IZO has a large amount of deep defect states that can be attributed to oxygen deficiency states resulting in instability in such TFTs. To resolve this issue, the addition of gallium has been utilised to reduce the oxygen deficiency state density making a-IGZO a suitable semiconducting material for TFTs. There is some evidence however that gallium doping leads to an increased device photosensitivity to visible light, a rather undesirable effect when they are used in flat panel displays.
In order to address the above-mentioned stability issues we have investigated TFTs employing solution processed tungsten-doped Indium Oxide (In2O3:W). The films were deposited by spray coating at 350 oC from InCl3 and WCl5 blends in methanol and characterised by X-ray diffraction, AFM, UV-Vis absorption spectroscopy and field effect measurements. TFTs that employed Al2O3 gate dielectrics, In2O3:W semiconducting channels (with various W content) and gold source and drain contacts underwent negative bias stress for 6000 s, and showed excellent stability characteristics such as a small decrease of the threshold voltage (from 2.3 V to 2.0 V) without significantly decreasing the electron mobility - decreased for 16 to 14 cm2/Vs.